Method and device for protecting a cathode ray tube in an image displaying device by using a brightness control circuit

Abstract

A method and device utilizes a brightness control circuit for protecting a cathode ray tube in an image displaying device. The displaying device has an image signal amplifier, a cathode ray tube, and a brightness control circuit. The cathode ray tube has a screen, an electron gun, and an anode for collecting an electron beam emitted onto the screen to produce an anode current. The brightness control circuit is electrically connected to a control end of the image signal amplifier for controlling the amplification magnitude of the image signal amplifier and electrically connected with the anode of the cathode ray tube via a flyback transformer, wherein when the incoming image signals make the image picture shown on the screen too bright, the anode current of the anode will be increased accordingly, and the brightness control circuit will reduce the amplification magnitude of the image signal amplifier at the same time according to the increase of the anode current so as to reduce the anode current. The brightness control circuit comprises an adjusting circuit electrically connected with the control end of the image signal amplifier for adjusting the brightness of the image picture of the screen.

What is claimed is:  
     
       1. A method for adjusting the brightness of a displaying device, the displaying device comprising: 
       an image signal amplifier for amplifying incoming image signals;  
       a cathode ray tube comprising a screen at its front end, an electron gun at its rear end for projecting and controlling an electron beam according to the amplified image signals onto the screen to create an image picture, and an anode for collecting the electron beam emitted onto the screen to produce an anode current; and  
       a brightness control circuit electrically connected to a control end of the image signal amplifier for controlling the amplification magnitude of the image signal amplifier and electrically connected with the anode of the cathode ray tube via a flyback transformer which is used for providing the anode with the anode current wherein when the incoming image signals make the image picture shown on the screen too bright, the anode current of the anode will be increased accordingly, and the brightness control circuit will reduce the amplification magnitude of the image signal amplifier at the same time according to the increase of the anode current so as to reduce the anode current, and wherein the brightness control circuit comprises an adjusting circuit electrically connected with the control end of the image signal amplifier for adjusting the brightness of the image picture of the screen;  
       the method comprising: 
       using a brightness detector to detect the brightness of the image picture of the screen, and  
       using the adjusting circuit to adjust the brightness of the image picture until the brightness detected by the brightness detector reaches a predetermined brightness value.  
     
     
       2. The method of  claim 1  wherein the brightness control circuit comprises a first resistor having a first end and a second end, and a voltage source electrically connected with the first end of the first resistor wherein the flyback transformer and the control end of the image signal amplifier are electrically connected with the second end of the first resistor and wherein when the anode current of the anode is increased, the voltage at the second end of the first resistor will be reduced because of the increased anode current passing through the first resistor from the voltage source, and the amplification magnitude of the image signal amplifier will be reduced in the same time according to the reduction of the voltage at the second end of the first resistor. 
     
     
       3. The method of  claim 2  wherein the brightness control circuit further comprises a noise filter electrically connected between the second end of the first resistor and a ground port for filtering electric noises contained in the anode current. 
     
     
       4. The method of  claim 3  wherein the noise filter is a capacitor. 
     
     
       5. The method of  claim 2  wherein the adjusting circuit is electrically connected between the second end of the first resistor and a ground port for adjusting the voltage at the second end of the first resistor. 
     
     
       6. The method of  claim 5  wherein the adjusting circuit employs a variable resistor for adjusting the voltage at the second end of the first resistor. 
     
     
       7. The method of  claim 5  wherein the adjusting circuit comprises a switch and a second resister connected in series and the switch and second resistor are connected between the second end of the first resistor and the ground port, and the adjusting circuit further comprises a micro-controller for controlling on-and-off of the switch using a pulse-width-modulation method to adjust the voltage at the second end of the first resistor. 
     
     
       8. A displaying device comprising: 
       an image signal amplifier for amplifying incoming image signals;  
       a cathode ray tube comprising a screen at its front end, an electron gun at its rear end for projecting and controlling an electron beam according to the amplified image signals onto the screen to create an image picture, and an anode for collecting the electron beam emitted onto the screen to produce an anode current; and  
       a brightness control circuit electrically connected with a control end of the image signal amplifier for controlling the amplification magnitude of the image signal amplifier and electrically connected with the anode of the cathode ray tube via a flyback transformer which is used for providing the anode with the anode current;  
       wherein the brightness control circuit comprises a first resistor having a first end and a second end and a voltage source electrically connected with the first end of the first resistor wherein the flyback transformer and the control end of the image signal amplifier are electrically connected with the second end of the first resistor and wherein when the incoming image signals make the image picture shown on the screen too bright, the anode current of the anode will be increased accordingly, and the brightness control circuit will reduce the amplification magnitude of the image signal amplifier at the same time according to the increase of the anode current so as to reduce the anode current. 
     
     
       9. The displaying device of  claim 8  wherein the brightness control circuit comprises an adjusting circuit electrically connected between the second end of the first resistor and a ground port for adjusting the voltage at the second end of the first resistor. 
     
     
       10. The displaying device of  claim 9  wherein the adjusting circuit comprises a variable resistor for adjusting the voltage at the second end of the first resistor. 
     
     
       11. The displaying device of  claim 9  wherein the adjusting circuit comprises a switch and a second resister connected in series and the switch and second resistor are connected between the second end of the first resistor and the ground port, and the adjusting circuit further comprises a micro-controller for controlling the on-and-off of the switch by using a pulse-width-modulation method to adjust the voltage at the second end of the first resistor. 
     
     
       12. The displaying device of  claim 8  wherein the brightness control circuit further comprises a noise filter electrically connected between the second end of the first resistor and a ground port for filtering electric noises contained in the anode current. 
     
     
       13. The displaying device of  claim 12  wherein the noise filter is a capacitor.